The reactive-banana package

The current focus of this library is to implement
a subset of the semantic model for functional reactive programming
pioneered by Conal Elliott.

Moreover, this library can hooked into any
existing event-based framework.
It is especially useful in conjunction with existing
GUI frameworks like wxHaskell or gtk2hs.

This also means that your code can be a mix of FRP and imperative parts.
Bored of programming imperative GUIs? Write some parts with FRP!
Don't know how to express something with FRP?
Switch back to imperative style!

In the spectrum of possible FRP implementations,
this one features simple semantics but modest expressivity.
Predicting space & time usage should be easy.

Stability forecast:
Known inefficiencies that will be addressed.
No semantic bugs expected.
Significant API changes are likely in future versions.